The main rotor of a rotorcraft serves to provide rotorcraft with lift, and indeed with propulsion. Conventionally, such a main rotor driven by an appropriate power plant comprises a rotor mast that sets a plurality of blades into rotation by means of a rotor hub.
In order to control the movement of the rotorcraft, the pitch of the blades of the main rotor is controlled, i.e. their angle of aerodynamic incidence is controlled. Under such circumstances, the blade pitch is adjustable by means of pitch control rods and a set of cyclic swashplates surrounding the rotor mast, the cyclic swashplates comprising in principle a rotary swashplate connected to the pitch control rods and a non-rotary swashplate connected to the flight controls.
The non-rotary swashplate is usually situated beneath the rotary swashplate and it imparts its movements along the axis of rotation of the rotor to the rotary swashplate. Thus, the rotary swashplate follows all of the movements of the non-rotary swashplate and transmits those movements to the blades via the pitch control rods.
Consequently, e.g. by using a plurality of servo-controls connected to the structure of the rotorcraft and to the non-rotary swashplate, the non-rotary and rotary swashplates are in a position to be moved in translation along the axis of rotation of the rotor mast, and also to be tilted relative to the rotor mast. Usually, movements in translation and in tilting are delivered using a device having a mast ball joint centered on the axis of rotation of the rotor and slidable along a stationary structural element that surrounds the rotor mast.
The non-rotary swashplate is then mounted in oscillating manner on the mast ball joint so as to be capable of being tilted and moved in translation relative to the rotor mast. In addition, the non-rotary swashplate is secured to the structure of the rotorcraft via at least one stationary scissors link that consequently prevents it from turning about the axis of rotation of the rotor.
The rotary swashplate of the set of cyclic swashplates is then connected to the non-rotary swashplate by a member enabling:                the rotary swashplate to be secured to the non-rotary swashplate in translation along the axis of rotation of the rotor;        the rotary swashplate to tilt about the mast ball joint jointly with the non-rotary swashplate; and        the rotary swashplate to rotate about the axis of rotation jointly with the rotor.        
To this end, the rotary swashplate is provided with at least one rotary scissors link connected to the rotor mast, possibly by the hub of the main rotor, the mast rotor driving rotation of the rotary swashplate about the axis of rotation.
A scissors link, whether rotary or non-rotary, generally comprises two hinged arms. More precisely, each scissors link comprises a primary arm and a secondary arm that are hinged to each other by a first hinge, the primary arm being connected via a second hinge to the rotor mast or to the structure, as appropriate, while the secondary arm is connected to the rotary swashplate by a third hinge.
Although effective, it is found that the first, second, and third hinges are subjected to high levels of wear requiring expensive and repeated maintenance actions.
To remedy that, scissors links are often overdimensioned, and thus end up being heavy and expensive to fabricate.
In addition, scissors links occupy a large amount of space, given the movements they must be free to make.
Document FR 2 768 996 thus seeks to replace the rotary scissors link by means that are lightweight, that are inexpensive to fabricate, and that generate less aerodynamic drag.
The set of cyclic swashplates then includes drive means constituting an alternative to the rotary scissors link and provided with two diametrically rigid arms, each rigid arm being firstly secured to the rotor mast and secondly connected by point connection means to the rotary swashplate.
More precisely, each arm is provided with a U-shaped section defining a rigid drive track in which there is received a finger of the rotary swashplate. The combination of the finger and the rigid track then constitutes point connection means.
It should be observed that in order to co-operate with the rigid drive track, in different variants the finger has one wheel, a pair of wheels, a sliding shoe, or indeed a sliding shoe and a wheel.
The solution of document FR 2 768 996 is advantageous.
Nevertheless, the space occupied by that solution continues to be considerable. In addition, there is a risk of frost forming on the rigid drive tracks and that can disturb the operation of the point connection means.